Through injury or diseases, human or animal lungs can become too weak to sustain a sufficient flow of oxygen to the body and to remove adequate amounts of expired carbon dioxide. Under these circumstances, it is often necessary to aid the lungs through forms of mechanical assistance, such as mechanical ventilation.
In a common form, mechanical ventilation involves the introduction of an endotracheal tube and, in some cases, a small, open-ended catheter within that tube, into the trachea of a human or animal. The distal ends of the endotracheal tube and/or catheter are positioned to rest at or slightly above the carina of the lungs. A well-humidified oxygen/air mixture is then introduced through the endotracheal tube and/or catheter to provide oxygen to the lungs. In less severe circumstances, the oxygen/air mixture can be supplied through the endotracheal tube and/or catheter using continuous positive airway pressure (CPAP). Where CPAP is used, the patient will use his or her own lung power to exhale the expired gas. In more severe circumstances, it is necessary to use mechanically controlled ventilation with a positive end expiratory pressure (PEEP).
One of the drawbacks of inserting an endotracheal tube and/or catheter into the trachea of a patient is that it reduces the lumen of the tracheal passageway and thus, without mechanical assistance, would make it more difficult for the patient to breathe. This situation is exacerbated if the endotracheal tube has a thick wall. To the extent the endotracheal tube and/or catheter is removing space from the tracheal passageway, it increases airway resistance. This airway resistance can be reduced by increasing the internal diameter of the endotracheal tube, but at a cost of increasing dead space where expired carbon dioxide gas can accumulate and be inhaled during the next breath.
There have been a number of attempts in the art to alleviate these airway resistance and dead space problems. In the inventor's earlier U.S. Pat. No. 5,429,127, which is incorporated herein by reference, a two stage ultra-thin walled endotracheal tube is disclosed which fits snugly against the contours of the trachea and uses a thin reinforcing wire to allow the endotracheal tube to be formed as thinly as possible. The ultra-thin walled endotracheal tube is effective in lowering the airway resistance as compared with thicker conventional endotracheal tubes. Also, in the inventor's earlier U.S. Pat. No. 5,687,714, a method is disclosed for preventing the distal end of an endotracheal tube catheter from becoming clogged with mucus and thereby unable to deliver fresh air to the lungs. By assuring that fresh air is delivered to the lungs, this invention reduces endotracheal tube dead space. While these inventions certainly represent important steps in the development of the tracheal ventilation art, more can still be done to address the airway resistance and dead space problems.